Batch process for the manufacture of a methanolic formaldehyde solution by depolymerization of paraformaldehyde

Abstract

A batch process for the preparation of a methanolic formaldehyde solution by depolymerization of paraformaldehyde in the presence of methanol and water, the process comprising the steps of: (a) providing a mixture comprising paraformaldehyde, water, and methanol, (b) subjecting the mixture obtained in step (a) to a first heating step, wherein the mixture is kept in a temperature range of from 50 to 90°C for a period of 5 to 300 minutes, (c) subjecting the mixture obtained in step (b) to a second heating step, wherein the mixture is kept in a temperature range of from 100 to 130 °C for a period of 0.1 to 48 hours.

Description

[0001] Batch process for the manufacture of a methanolic formaldehyde solution by depolymerization of paraformaldehyde

[0002] The invention concerns a batch process for the preparation of a methanolic formaldehyde solution by depolymerization of paraformaldehyde in the presence of methanol and water. The invention further concerns a process for preparing N-methylmorpholine, a process for preparing N-methylmorpholine oxide and a process for preparing pentamethyl diethylenetriamine.

[0003] Formaldehyde is manufactured by subjecting methanol to selective oxidation on a large scale. It is available as aqueous solution, methanolic solution or paraformaldehyde. Since paraformaldehyde is a solid, it cannot be easily used in any continuous process. Aqueous and methanolic formaldehyde can be used in both batch and continuous processes. The usage of methanolic formaldehyde can have certain advantages over aqueous formaldehyde. For instance, it has been recently found that in the NMM production yellowing can be avoided when methanolic formaldehyde is used. Another advantage resides in the fact that the separation of methanol from the reaction product is less energy demanding than the separation of water. This is due to the lower boiling point of methanol. However, the availability of methanolic formaldehyde solution is limited which is mainly because its production from methanol is more complex than the production of aqueous formaldehyde solution (see US3629997). Thus, there is a low availability of methanolic formaldehyde solution.

[0004] Paraformaldehyde can be synthesized from an aqueous formaldehyde solution via polymerization of the formaldehyde. It typically forms as a white precipitate. Its chemical formula is OH(CH2O)nH with n typically being in the range from 8 to 100.

[0005] Formaldehyde is used for instance for the preparation of N-methylmorpholine (NMM) and pentamethyl diethylentriamine (PMDETA) by reductive amination of formaldehyde with morpholine (MO) and diethylentriamine (DETA), respectively, in the presence of hydrogen and a hydrogenation catalyst. NMM and PMDETA are used as catalysts in polyurethane production. It was found that it is advantageous to employ formaldehyde as a methanolic formaldehyde solution.

[0006] CN 110627654 A teaches a batch process for the methylation of amines being selected from ethylenediamine, cyclohexylamine, aniline or benzylamine using paraformaldehyde.

[0007] CN 111675677 B teaches a batch process for the manufacture of N-methylmorpholine using paraformaldehyde but no metal catalyst or reducing agent.

[0008] CN 106957232 A teaches a batch process for the manufacture of an N-monomethylamine compound using paraformaldehyde.

[0009] According to GB 737,023, an aqueous solution of formaldehyde is distilled to form formaldehyde vapor which contains water. The formaldehyde vapor is mixed with alcohol vapor, for example methanol vapor, which absorbs the water and is condensed with it in the first stage, while part of the formaldehyde vapor is only later condensed with further methanol in a second stage to form a product which has a high formaldehyde concentration, namely from 70% or more. This known method is very complicated. Separating the water vapor from the formaldehyde by the addition of methanol vapor and condensation requires a cumbersome device.

[0010] It is an object of the present invention to provide a simple and economic process for the preparation of a methanolic formaldehyde solution.

[0011] The object is solved by a batch process for the preparation of a methanolic formaldehyde solution by depolymerization of paraformaldehyde in the presence of methanol and water, the process comprising the steps of:

[0012] (a) providing a mixture comprising paraformaldehyde, water, and methanol,

[0013] (b) subjecting the mixture obtained in step (a) to a first heating step, wherein the mixture is kept in a temperature range of from 50 to 90°C for a period of 5 to 300 minutes,

[0014] (c) subjecting the mixture obtained in step (b) to a second heating step, wherein the mixture is kept in a temperature range of from 100 to 130 °C for a period of 0.1 to 48 hours.

[0015] The inventors have found that the application of the two heating steps (b) and (c) results in an improved process for the manufacture of a methanolic formaldehyde solution.

[0016] In the context of the present invention, the term “heating” means the supply of thermal energy in the form of heat. For instance, one can supply so much heat, that the temperature of the mixture increases. One can also supply heat in an amount required to compensate the heat dissipated to the environment and / or to a respective condenser with which a suitable batch reactor is typically equipped.

[0017] Without wanting to be bound by any theory, it is believed that keeping the mixture in a temperature range of from 50 to 90°C for a period of 5 to 300 minutes as per step (b) results in the formation of a solution comprising the hemiacetal of formaldehyde with methanol and / or higher polyoxymethylene homologues thereof, which are higher boiling compounds than methanol itself. However, the depolymerization of paraformaldehyde is incomplete in this temperature range. Full depolymerization is achieved in the higher temperature range of from 100 to 130 °C according to step (c). Due to the preceding formation of the higher boiling mixture comprising hemiacetal of formaldehyde and methanol (hereinafter also referred to as “hemiacetal”) and / or higher polyoxymethylene homologues thereof, methanol evaporation is very much reduced in the higher temperature range. However, when heating the mixture of paraformaldehyde, water, and methanol directly to a temperature range of from 100 to 130 °C, methanol is constantly evaporating. This requires a very high condenser load which is needed to ensure a significant amount of methanol (solvent) in the reactor. A high condenser load means that a large amount of thermal energy is removed per unit of time and, thus, is energetically inefficient. Moreover, it may be critical in the context of operational safety. For instance, in case of a power failure, as a result of which the condenser does not operate properly, methanol in the reaction mixture evap- orates very rapidly (because of the high temperatures of 100 to 130 °C in the mixture). Without the presence of enough solvent in the mixture the likelihood that superheating and other unwanted events occur, significantly increases. Thus, intensive monitoring of the reaction would be required in such case.

[0018] As outlined above, it is key to the present invention that the mixture is first kept in a temperature range of from 50 to 90°C. It is believed that in such temperature range the hemiacetal formation and / or formation of higher polyoxymethylene homologues thereof occurs at a significant rate. To ensure that enough hemiacetal and / or higher polyoxymethylene homologues thereof are formed, the mixture needs to be kept in such temperature range for at least 5 minutes. One way to realize step (b) is to directly heat the mixture to a specific temperature in the range of from 50 to 90°C (for instance 80°C) and keep it at that temperature for a certain period (for instance 150 minutes) in accordance with step (b). Another way to realize step (b) is to gently heat the mixture so that temperature slowly rises. For instance, one could heat the mixture so that the temperature rises from 50 to 90°C during a period of 90 minutes. In principle, it would also be possible to directly heat to a temperature of fer instance 70°C and then slowly heat to a temperature of fer instance 85°C for a period of 100 minutes. It is further to be noted that heating can also be interrupted, although this is not preferred. For instance, it would not be critical and therefore in accordance with the present invention, if the reaction is for instance directly heated to a temperature of 85°C, kept at this temperature for 60 minutes, and thereafter cooled (by non-heating) to 60°C for a period of 60 minutes.

[0019] The above equally applies to step (c).

[0020] Preferably the mixture is stirred in step (b) as well as in step (c).

[0021] Steps (b) and (c) can be carried out for instance with an average heating rate of from 2 to 200 °C / h, preferably with an average heating rate of from 5 to 100 °C / h, more preferably with an average heating rate of from 10 to 50 °C / h

[0022] The absolute pressure is in general in the range of 0.5 to 20 bar, preferably 0.5 to 10 bar, more preferably 0.5 to 5 bar, particularly preferably 0.8 to 3 bar, especially 0.9 to 2 bar, for example 1 .0 to 1.5 bar.

[0023] The mixture provided in step (a) in general comprises 20 to 69 wt.-% paraformaldehyde, 30 to 69 wt.-% methanol, and 1 to 20 wt.-% water. Preferably, the mixture provided in step (a) comprises paraformaldehyde in the range of from 35 to 65 wt.-%, methanol in the range of from 30 to 45 wt.-% and water in the range of from 5 to 20 wt.-%. Even more preferably, the mixture provided in step (a) comprises paraformaldehyde in the range of from 40 to 60 wt.-%, methanol in the range of from 30 to 45 wt.-% and water in the range of from 5 to 15 wt.-%. The mixture provided in step (a) in general exists at ambient temperature. This depends on the location of the respective production facility. Typically, it has a temperature in the range of from 1 to 49 °C, preferably from 5 to 45°C.

[0024] The temperature range according to step (b) is in general of from 60 to 90 °C, preferably 70 to 90 °C, more preferably 75 to 85 °C. In general, a higher temperature range is preferred because it provides for a higher formation rate of the hemiacetal and higher polyoxymethylene homologues thereof. As a result, the period in which such temperature range is realized can be shorter.

[0025] The period according to step (b) is in general 30 to 250 minutes, preferably 60 to 200 minutes, more preferably 90 to 200 minutes, even more preferably 120 to 200 minutes.

[0026] The temperature range according to step (c) is in general of from 110 to 130 °C, preferably 110 to 125°C, more preferably 110 to 120 °C.

[0027] The period according to step (c) is in general 0.5 to 36 hours, preferably 1 to 24 hours, more preferably 1 to 12 hours, even more preferably 2 to 12 hours.

[0028] The reaction is preferably performed in a reactor, typically a STR (stirred tank reactor, also referred to as agitated vessel). It is typically performed under air or under nitrogen atmosphere, wherein a nitrogen atmosphere is preferred. In accordance with the present invention, the reactor is operated in a batch mode, meaning that all components of the mixture are added to the vessel and the agitation is started. A respective stirrer having a suitable geometry to achieve thorough mixing can be easily selected by the person having ordinary skill in the art. Such reactor is preferably equipped with a condenser. A condenser is a device that is used to condense vapor into liquid using a cooling agent that may be selected from water, air or brine. Suitable condensers can be easily selected by the person having ordinary skill in the art.

[0029] In the methanolic formaldehyde solution obtained according to the invention, the formaldehyde may exist in different forms. For instance, a certain amount, in general the major part, of formaldehyde exists as a hemiacetal (resulting from formaldehyde and methanol also referred to as hemiformal or 1 -methoxy-methanol) or polyoxymethylene having the formula HO-[CH2O]n-CH3 with n being an integer typically in the range from 2 to 10. The weight percentages (“wt.-%”) specified herein refer to the “theoretical” amount of formaldehyde, methanol, and water, thus, neglecting any potential reactions among formaldehyde, methanol, and water.

[0030] Preferably, the methanolic formaldehyde solution obtained according to the present invention comprises formaldehyde in the range of from 20 to 69 wt.-%, methanol in the range of from 30 to 69 wt.-% and water in the range of from 1 to 20 wt.-%. The wt.-% is based on the total mass of the methanolic formaldehyde solution. More preferably, the methanolic formaldehyde solution comprises formaldehyde in the range of from 35 to 65 wt.-%, methanol in the range of from 30 to 45 wt.-% and water in the range of from 5 to 20 wt.-%.

[0031] Even more preferably, the methanolic formaldehyde solution comprises formaldehyde in the range of from 40 to 60 wt.-%, methanol in the range of from 30 to 45 wt.-% and water in the range of from 5 to 15 wt.-%.

[0032] In a preferred embodiment, the amount of formaldehyde, methanol, and water in the methanolic formaldehyde solution is > 90 wt.-%, preferably > 95 wt.-%, more preferably > 98 wt.-%, even more preferably > 99 wt.-%, particularly preferably > 99.5 wt.-%.

[0033] It is another object of the present invention to provide for a simple and economic process for the preparation of N-methylmorpholine (NMM). It is a further object of the present invention to provide for a simple and economic process for the preparation of N-methylmorpholine oxide (NMMO). It is further object of the present invention to provide for a simple and economic process for the preparation of pentamethyl diethylentriamine.

[0034] The invention also relates to a process for the preparation of N-methylmorpholine (NMM) comprising the steps of

[0035] (i) providing formaldehyde as a methanolic formaldehyde solution obtained by the process of the invention as described above,

[0036] (ii) providing morpholine,

[0037] (iii) subjecting formaldehyde provided in step (i) and morpholine provided in step (ii) to a continuous reductive amination in the presence of hydrogen and a heterogenous hydrogenation catalyst, which is immobilized in the reactor, to obtain N-methylmorpholine.

[0038] The methanolic formaldehyde solution fed to step (i) is prepared by the process of the invention as described above and comprises formaldehyde, methanol and water in the ranges indicated above.

[0039] The process is preferably carried out continuously.

[0040] Key for this process is the provision of methanolic formaldehyde solution based on paraformaldehyde by using the simple and economic process of the invention as described above.

[0041] In a preferred embodiment the heterogenous hydrogenation catalyst is used as a fixed bed catalyst.

[0042] This process for the manufacture of NMM is more efficient than a process using paraformaldehyde because the amination can be conducted continuously. A respective process using paraformaldehyde in the amination cannot be operated continuously (because paraformaldehyde is a solid). Since the amination requires a heterogeneous catalyst, the latter needs to be separat- ed which is technically and economically less efficient than using an immobilized catalyst as per step (iii). Moreover, the space-time yield of the continuous process is superior (i.e. higher) compared to the batch process.

[0043] In a preferred embodiment, methanol is separated from N-methylmorpholine obtained in step (iii) and recycled to step (a) of the methanolic formaldehyde production process according to the present invention. In this way, the combination of the process for the manufacture of methanolic formaldehyde solution and the NMM production becomes even more efficient because the methanol can be continuously reused.

[0044] In general, morpholine provided in step (ii) is prepared by reacting diethylene glycol and ammonia in the presence of hydrogen and a heterogeneous hydrogenation catalyst. The preparation of morpholine from diethylene glycol and ammonia is described for instance in WO2011 / 067199 A1 , W02008 / 037587 A1 , WO 2008 / 037589 A1 and WO 2008 / 037590 A1 (all BASF).

[0045] The continuously fed formaldehyde solution is a methanolic formaldehyde solution prepared according to the invention.

[0046] Usually, the reaction temperature is in the range of from 30 to 300°C, preferably from 30 to 250°C, more preferably from 30 to 200°C. The reaction temperature is even more preferably from 60 to 150°C, particularly preferably from 80 to 130°C, especially from 90 to 130°C.

[0047] Unless not explicitly provided otherwise, all pressures in this application refer to the absolute pressure.

[0048] The reaction pressure is usually in the range of from 50 to 300 bar, preferably from 50 to 250 bar, more preferably from 50 to 200 bar, even more preferably from 60 bar to 150 bar, particularly preferably from 80 to 150 bar, especially from 90 to 140 bar.

[0049] The process for the preparation of N-methylmorpholine is conducted in the presence of a heterogeneous hydrogenation catalyst. The term heterogeneous catalyst designates a solid catalyst, preferably in the form of particles, which is brought into contact with the liquid reaction mixture comprising the starting materials and any intermediates and NMM already obtained.

[0050] Any heterogeneous catalyst that has sufficient hydrogenation activity can be used for the manufacture of NMM in accordance with the present invention. It may be a supported or an unsupported catalyst. An unsupported catalyst is preferred.

[0051] Preferably, the heterogeneous hydrogenation catalyst is devoid or substantially devoid of any palladium. The amount of palladium is preferably less than 0.5 wt.-%, preferably less than 0.05 wt.-%, more preferably less than 0.01 wt.-%, based on the total weight of the heterogeneous hydrogenation catalyst. The heterogeneous hydrogenation catalyst is installed in the reactor, preferably as fixed bed.

[0052] The heterogeneous hydrogenation catalyst may comprise cobalt.

[0053] Preferably it comprises cobalt and / or copper, more preferably cobalt, copper and / or manganese, even more preferably cobalt, copper, manganese and / or molybdenum, particularly preferably cobalt, copper, manganese, molybdenum, and / or phosphorus. In any of the foregoing combinations preference is given to the “and” conjunction in any of the forgoing embodiments.

[0054] The heterogeneous hydrogenation catalyst can for instance be prepared by applying precipitation or impregnation methods. Suitable heterogeneous hydrogenation catalysts and respective methods for their production are for instance taught in EP 2043996 B1 , WO 2011 / 067200 A1 , WO 2011 / 067199 A1 and EP 2780109 B1 (all BASF).

[0055] In a very preferred embodiment, the heterogeneous hydrogenation catalyst comprises

[0056] 5 to 90 wt.-%, preferably 10 to 60 wt.-%, cobalt, 1 to 40 wt.-%, preferably 2 to 30 wt.-%, copper, 0.1 to 30 wt.-%, preferably 1 to 10 wt.-%, manganese, 0.1 to 30 wt.-%, preferably 1 to 10 wt.-%, molybdenum, and 0.05 to 30 wt.-%, preferably 0.1 to 5 wt.-%, phosphorus, based on the total weight of the heterogeneous hydrogenation catalyst.

[0057] The preparation of such catalysts is for instance taught in DE 2321101 (BASF). Accordingly, the catalyst is obtained by precipitation, followed by calcination. The catalyst thus obtained is activated by reduction in a hydrogen stream. It is to be noted, that any “wt.-%” as specified herein with respect to the composition of the heterogeneous hydrogenation catalyst refers the heterogeneous hydrogenation catalyst after the last of any heat treatments (for instance calcination) and prior to its reduction with hydrogen.

[0058] It follows from the nature of the preparation method, that the respective metals at least partially exist in an oxidized from. Nonetheless, the presence of a certain amounts of such metals in elementary form is not excluded. For instance, in the course of the preparation, one could, besides using respective metal nitrites, also apply certain amount(s) of respective metal(s) in elementary form. Usually, more than 90 wt.-%, preferably more than 95 wt.-%, more preferably more than 99 wt.-% (or even more than 99.5 wt.-%) of any respective metal exists in oxidized from. The phosphorus usually exists substantially in an oxidized form. Usually, one would not apply elementary phosphor in the catalyst preparation, but phosphorus in an oxidized form only (in particular phosphoric acid). Moreover, the formation of elementary phosphorus during precipitation or calcination is unlikely to happen. Thus, preferably more than 99 wt.-%, more preferably more than 99.5 wt.-%, even more preferably more than 99.9 wt.-% of the respective phosphorus exist in oxidized form. The heterogeneous hydrogenation catalyst preferably also contains oxygen. In a preferred embodiment the heterogeneous hydrogenation catalyst comprises oxygen and the cumulated amount of oxygen, cobalt, copper, manganese, molybdenum, phosphorus, and cobalt is > 80 wt.-%, preferably > 90 wt.-%, more preferably > 95 wt.-% even more preferably > 97 wt.-%, particularly preferably > 98 wt.-%, based on the total weight of the heterogenous hydrogenation catalyst.

[0059] The invention further relates to a process for preparing N-methylmorpholine oxide (NMMO), comprising the steps of:

[0060] (i) preparing N-methylmorpholine in accordance with the process of the invention as described above, and

[0061] (ii) subjecting the N-methylmorpholine obtained in step (i) to an oxidation reaction to obtain N-methylmorpholine oxide.

[0062] Oxidation step (ii) comprises reacting N-methylmorpholine with a less than stoichiometric amount of aqueous hydrogen peroxide in an aqueous medium in the presence of carbon dioxide as promotor.

[0063] In a preferred embodiment, oxidation step (ii) comprises reacting N-methylmorpholine with a less than stoichiometric amount of aqueous hydrogen peroxide in an aqueous medium while imposing on the aqueous medium a vapor space having a carbon dioxide partial pressure p (CO2) of less than 0.75 bar absolute, preferably less than 0.20 bar absolute. Although carbon dioxide is an effective promoter for the conversion of a tertiary amine into its amine oxide, applicants have found that amounts of free carbon dioxide in excess of a promoting amount can lead to undesired discoloration.

[0064] In an embodiment, the initial concentration of N-methylmorpholine in the aqueous medium, that is the concentration of N-methylmorpholine prior to the addition of hydrogen peroxide, is in the range of from 40 to 95 vol.-%, preferably 60 to 85 vol.-%. Any aqueous hydrogen peroxide can be used. In view of practical considerations, the concentration of hydrogen peroxide in the aqueous hydrogen peroxide that is added to the aqueous medium is in the range of from 10 to 70 wt.-%, preferably 29 to 51 wt.-%.

[0065] The process is preferably carried out continuously.

[0066] The invention further relates to a process for the preparation of pentamethyl diethylentriamine (PMDETA) comprising the steps of

[0067] (i) providing formaldehyde as a methanolic formaldehyde solution obtained by the process of the invention as described above,

[0068] (ii) providing diethylentriamine, (iii) subjecting formaldehyde provided in step (i) and diethylentriamine (DETA) provided in step (ii) to reductive amination in the presence of hydrogen and a hydrogenation catalyst to obtain pentamethyl diethylentriamine.

[0069] The methanolic formaldehyde solution fed to step (i) is prepared by the process of the invention as described above and comprises formaldehyde, methanol and water in the ranges indicated above.

[0070] The process is preferably carried out continuously.

[0071] Key for this process is the provision of methanolic formaldehyde solution based on paraformaldehyde by using the simple and economic process of the invention as described above.

[0072] In a preferred embodiment the heterogenous hydrogenation catalyst is used as a fixed bed catalyst.

[0073] This process for the manufacture of PM DETA is more efficient than a process using paraformaldehyde because the amination can be conducted continuously. A respective process using paraformaldehyde in the amination cannot be operated continuously (because paraformaldehyde is a solid). Since the amination requires a heterogeneous catalyst, the latter needs to be separated which is technically and economically less efficient than using an immobilized catalyst as per step (iii). Moreover, the space-time yield of the continuous process is superior (i.e. higher) compared to the batch process.

[0074] In a particular preferred embodiment, the molar ratio of formaldehyde to DETA is in the range of from 4.5:1 to < 5.9:1.

[0075] In a preferred embodiment, PMDETA is partially recycled to the reductive amination of DETA and formaldehyde. Preferably, the weight ratio of recycled PMDETA to the combined amount of DETA and methanolic formaldehyde solution being fed to the one or more reactor(s) is in the range of from 1 :1 to 10:1 , preferably from 2:1 to 8:1.

[0076] The reaction temperature is in general in the range of from 30 to 300 °C, preferably from 30 to 250 °C, more preferably from 30 to 200 °C, even more preferably from 60 to 150 °C, particularly preferably from 80 to 130 °C, especially from 90 to 130 °C.

[0077] The reaction pressure is in the range of from 50 to 300 bar, preferably from 50 to 250 bar, more preferably from 50 to 200 bar, even more preferably from 60 bar to 150 bar, particularly preferably from 80 to 150 bar, especially from 90 to 140 bar.

[0078] The heterogeneous hydrogenation catalyst preferably comprises cobalt and / or copper. Preferred heterogeneous hydrogenation catalyst are those described above in connection with the preparation of N MM. A particular preferred catalyst comprises 5 to 90 wt.-%, preferably 10 to 60 wt.-%, cobalt, 1 to 40 wt.-%, preferably 2 to 30 wt.-%, copper, 0.1 to 30 wt.-%, preferably 1 to 10 wt.-%, manganese, 0.1 to 30 wt.-%, preferably 1 to 10 wt.-%, molybdenum, and 0.05 to 30 wt.-%, preferably 0.1 to 5 wt.-%, phosphorus, based on the total weight of the heterogeneous hydration catalyst.

[0079] The following examples only serve for the purpose of the illustration of the present invention and shall therefore not limit it in whatsoever kind.

[0080] EXAMPLES

[0081] Example 1 :

[0082] Water containing paraformaldehyde, having a paraformaldehyde content of about 96 wt.-% (57wt.-%) was added to a stirred vessel equipped with a condenser. Water was added (8 wt.-%) and the reactor set under nitrogen atmosphere. MeOH (35 wt.-%) was added and stirring initiated (100 rpm). The mixture was heated to 80 °C and stirred for 150 min, then at 115 °C for 240 min. After cooling, a clear solution, containing 55 wt.-% formaldehyde was obtained (measured via UV-Vis spectroscopy as free formaldehyde).

[0083] Example 2:

[0084] Water containing paraformaldehyde, having a paraformaldehyde content of about 77 wt.-% (55 wt.-%) was added to a stirred vessel. Water was added (10 wt.-%) and the reactor set under nitrogen atmosphere. MeOH (35 wt.-%) was added and stirring initiated (100 rpm). The mixture was heated to 80 °C and stirred for 150 min, then at 115 °C for 240 min. After cooling, a clear solution, containing 42.4 wt.-% formaldehyde was obtained (measured via UV-Vis spectroscopy as free formaldehyde).

[0085] Example 3:

[0086] Water containing paraformaldehyde, having a paraformaldehyde content of about 92 wt.-% (65 wt.-%) was added to a stirred vessel equipped with a condenser and the reactor set under nitrogen atmosphere. MeOH (35 wt.-%) was added and stirring initiated (100 rpm). The mixture was heated to 80 °C and stirred for 150 min, then at 115 °C for 240 min. After cooling, a clear solution, containing 60 wt.-% formaldehyde was obtained (measured via UV-Vis spectroscopy as free formaldehyde).

[0087] Example 4 (evidence of the formation of formaldehyde hemiacetal and higher polyoxymethylene homologues thereof): Water containing paraformaldehyde, having a paraformaldehyde content of about 96 wt.-% (57 wt.-%) was added to a stirred vessel equipped with a condenser. Water was added (8 wt.- %) and the reactor set under nitrogen atmosphere. MeOH (35 wt.-%) was added and stirring initiated (100 rpm). The mixture was heated to 60 °C and stirred for 120 min and a 13C NMR spectrum was measured. The spectrum indicates the formation of methoxymethanol (CAS = 4461-52-3; formaldehyde hemiacetal) and higher polyoxymethylene homologues thereof. There is no indication of higher molecular structures or free formaldehyde in the solution.

[0088] Example 5 (comparative):

[0089] Water containing paraformaldehyde, having a paraformaldehyde content of about 96 wt.-% (55 wt.-%) was added to a stirred vessel equipped with a condenser. Water was added (10 wt.-%) and the reactor set under nitrogen atmosphere. MeOH (35 wt.-%) was added and stirring initiated (100 rpm). The mixture was heated to 80 °C and stirred for 150 min + 240 min (i.e. overall 390 min). After cooling, a white suspension was obtained. This indicated that paraformaldehyde was not fully depolymerized. Using this suspension in a continuous setup is not feasible due to clogging of pumps and other equipment.

[0090] Discussion of Results:

[0091] When heating to a temperature in the range of 50 to 90°C depolymerization is not complete (see comparative Example 5). When directly heating to a temperature in the range of 100 to 130 °C, methanol is constantly evaporated (very high condenser load required). There is too much methanol in the gas phase. Thus, depolymerization does not run smoothly. First heating to 60 to 90 °C results in hemiacetal formation (i.e. transformation of methanol into a higher boiling compound). If that transformation has been completed, full depolymerization is achieved at the higher temperature of from 100 to 130°C.

Claims

Claims1 . A batch process for the preparation of a methanolic formaldehyde solution by depolymerization of paraformaldehyde in the presence of methanol and water, the process comprising the steps of:(a) providing a mixture comprising paraformaldehyde, water, and methanol,(b) subjecting the mixture obtained in step (a) to a first heating step, wherein the mixture is kept in a temperature range of from 50 to 90°C for a period of from 5 to 300 minutes,(c) subjecting the mixture obtained in step (b) to a second heating step, wherein the mixture is kept in a temperature range of from 100 to 130 °C for a period of from 0.1 to 48 hours.

2. The process according to claim 1 , wherein the temperature range according to step (b) is of from 60 to 90 °C, preferably from 70 to 90 °C, more preferably from 75 to 85 °C. .

3. The process according to claim 1 or 2, wherein the period according to step (b) from is 30 to 250 minutes, preferably from 60 to 200 minutes, more preferably from 90 to 200 minutes, even more preferably from 120 to 200 minutes.

4. The process according to any one of claims 1 to 3, wherein the temperature range according to step (c) is of from 110 to 130 °C, preferably from 110 to 125°C, more preferably from 110 to 120°C.

5. The process according to claim 4, wherein the period according to step (c) is from 0.5 to 36 hours, preferably from 1 to 24 hours, more preferably from 1 to 12 hours, even more preferably from 2 to 12 hours.

6. The process according to any one of claims 1 to 5, wherein the absolute pressure is in the range of from 0.5 to 20 bar, preferably from 0.5 to 10 bar, more preferably from 0.5 to 5 bar, particularly preferably from 0.8 to 3 bar, especially from 0.9 to 2 bar, for example from 1 .0 to 1.5 bar.

7. The process according to any one of claims 1 to 6, wherein the mixture provided in step (a) comprises 20 to 69 wt.-% paraformaldehyde, 30 to 69 wt.-% methanol, and 1 to 20 wt.- % water.

8. A process for the preparation of N-methylmorpholin comprising the steps of(i) providing formaldehyde as a methanolic formaldehyde solution obtained by the process of any one of claims 1 to 7,(ii) providing morpholine,(iii) subjecting formaldehyde provided in step (i) and morpholine provided in step (ii) to reductive amination in the presence of hydrogen and a hydrogenation catalyst to obtain N- methylmorpholine.

9. The process of claim 8, wherein morpholine provided in step (ii) is prepared by reacting diethylene glycol and ammonia in the presence of hydrogen and a heterogeneous hydrogenation catalyst.

10. A process for preparing N-methylmorpholine oxide, comprising the steps of:(i) preparing N-methylmorpholine in accordance with the process of claim 8 or 9, and(ii) subjecting the N-methylmorpholine obtained in step (i) to an oxidation reaction to obtain N-methylmorpholine oxide.11 . The process of claim 10, wherein the oxidation reaction of step (ii) comprises reacting N- methylmorpholine with a less than stoichiometric amount of aqueous hydrogen peroxide in an aqueous medium in the presence of carbon dioxide as promotor.

12. The process of claim 11 , wherein oxidation step (ii) comprises reacting N-methyl- morpholine with a less than stoichiometric amount of aqueous hydrogen peroxide in an aqueous medium while imposing on the aqueous medium a vapor space having a carbon dioxide partial pressure p (CO2) of less than 0.75 bar absolute, preferably less than 0.20 bar absolute.

13. A process for the preparation of pentamethyl diethylentriamine comprising the steps of(i) providing formaldehyde as a methanolic formaldehyde solution obtained by the process of any one of claims 1 to 7,(ii) providing diethylentriamine,(iii) subjecting formaldehyde provided in step (i) and diethylentriamine provided in step (ii) to reductive amination in the presence of hydrogen and a hydrogenation catalyst to obtain pentamethyl diethylentriamine.